Typically, charge pumps use a switching process to provide an output voltage that has a larger magnitude than an input voltage. Charge pumps are used in many contexts, e.g., in integrated circuits, peripheral circuits on flash memory, and other circuits, for generating the needed operating voltages from a lower supply voltage.
A number of charge pump designs, such as conventional Dickson-type charge pumps, are known in the art. FIG. 1 illustrates a typical four-stage Dickson charge pump device. The Dickson charge pump comprises diodes D1-D5 connected in series with coupling capacitors C1-C4, where each capacitor is connected to a node between the diodes D1-D5. The Dickson charge pump circuit also includes an output capacitor Cout. The input clock pulses, a ClkA and a ClkB, are out of phase with respect to each other, where the ClkA is applied to the capacitors C1 and C3, and the ClkB is applied to the capacitors C2 and C4. As can be appreciated by persons of ordinary skill in the art, each clock pulse with drive the output voltage by a multiplier of the input voltage.
If the input voltage for the charge pump is particularly low (e.g., 1V or lower), the charge pump, according to previous designs known in the art, would either fail to provide the requisite driving voltage due to switch conduction loss or alternately require a complex structure. Thus, providing charge pump circuits that would have minimal drain (as small as possible) on the power supply for their operation is of significant importance. The present trend toward ever lower supply voltages for integrated circuits can only increase this importance.
Therefore, it is important to provide new methods and circuits for a charge pump which can operate with input voltages as low as 1V or less.